Examination of the effects of excess microalgae availability on the disruption of mussel byssus secretion

The present study evaluated the effects of food availability on byssus secretion in the hard-shelled mussel Mytilus coruscus. Byssus production was evaluated, and foot tissue transcriptomes, the site of byssus production, were generated. The results showed that byssus secretion was disrupted in mussels fed high levels of microalgae (HFL, 88.8 mg/L day−1), compared to the control group (p < 0.05), and that more byssus production occurred in the HFL group during the recovery period. Byssus secretion was not affected in mussels fed low levels of microalgae (8.88 × 10−3 mg/L day−1), but the shedding of byssus filaments was significantly increased compared to the control mussels (p < 0.05). Transcriptome data of the foot tissue revealed that lysosome, FoxO signaling, and autophagy pathways involved in autophagic cell death and apoptosis were significantly affected (p < 0.05) and may explain differences in byssus growth under modified food availability in M. coruscus. High feed levels modified metabolic pathways, such as sphingolipid, tyrosine, and phenylalanine, and downregulated genes coding for mussel foot proteins, which may explain reduced byssus production. The study found that contrary to expectation increased food availability reduced mussel byssus production by altering foot metabolism and promoting autophagy of foot tissue.